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Colorectal Cancer Screening (PDQ®)

Patient Version
Last Modified: 12/16/2011

Colorectal Cancer Screening

Key Points for This Section


Tests are used to screen for different types of cancer.

Some screening tests are used because they have been shown to be helpful both in finding cancers early and decreasing the chance of dying from these cancers. Other tests are used because they have been shown to find cancer in some people; however, it has not been proven in clinical trials that use of these tests will decrease the risk of dying from cancer.

Scientists study screening tests to find those with the fewest risks and most benefits. Cancer screening trials also are meant to show whether early detection (finding cancer before it causes symptoms) decreases a person's chance of dying from the disease. For some types of cancer, finding and treating the disease at an early stage may result in a better chance of recovery.

Clinical trials that study cancer screening methods are taking place in many parts of the country. Information about ongoing clinical trials is available from the NCI Web site 1.

Studies show that screening for colorectal cancer helps decrease the number of deaths from the disease.

Four tests are commonly used to screen for colorectal cancer:

Fecal occult blood test

A fecal occult blood test (FOBT) is a test to check stool (solid waste) for blood that can only be seen with a microscope. Small samples of stool are placed on special cards and returned to the doctor or laboratory for testing. Blood in the stool may be a sign of polyps or cancer.

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Fecal Occult Blood Test (FOBT) kit; shows card, applicator, and return envelope.
Fecal Occult Blood Test (FOBT) kit to check for blood in stool.


A new colorectal cancer screening test called immunochemical FOBT (iFOBT) is being studied to see if it is better at finding advanced polyps or cancer than the FOBT.

Sigmoidoscopy

Sigmoidoscopy is a procedure to look inside the rectum and sigmoid (lower) colon for polyps, abnormal areas, or cancer. A sigmoidoscope is inserted through the rectum into the sigmoid colon. A sigmoidoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer.

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Sigmoidoscopy; shows sigmoidoscope inserted through the anus and rectum and into the sigmoid colon. Inset shows patient on table having a sigmoidoscopy.
Sigmoidoscopy. A thin, lighted tube is inserted through the anus and rectum and into the lower part of the colon to look for abnormal areas.


Barium enema

A barium enema is a series of x-rays of the lower gastrointestinal tract. A liquid that contains barium (a silver-white metallic compound) is put into the rectum. The barium coats the lower gastrointestinal tract and x-rays are taken. This procedure is also called a lower GI series.

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Barium enema procedure; shows barium liquid being put into the rectum and flowing through the colon. Inset shows person on table having a barium enema.
Barium enema procedure. The patient lies on an x-ray table. Barium liquid is put into the rectum and flows through the colon. X-rays are taken to look for abnormal areas.


Colonoscopy

Colonoscopy is a procedure to look inside the rectum and colon for polyps, abnormal areas, or cancer. A colonoscope is inserted through the rectum into the colon. A colonoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove polyps or tissue samples, which are checked under a microscope for signs of cancer.

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Colonoscopy; shows colonoscope inserted through the anus and rectum and into the colon. Inset shows patient on table having a colonoscopy.
Colonoscopy. A thin, lighted tube is inserted through the anus and rectum and into the colon to look for abnormal areas.


Studies have not shown that screening for colorectal cancer using digital rectal exam helps decrease the number of deaths from the disease.

A digital rectal exam (DRE) may be done as part of a routine physical exam. A digital rectal exam is an exam of the rectum. A doctor or nurse inserts a lubricated, gloved finger into the lower part of the rectum to feel for lumps or anything else that seems unusual. Study results have shown that there is no evidence to support DRE as a screening method for colorectal cancer.

New screening tests are being studied in clinical trials.

Virtual colonoscopy

Virtual colonoscopy is a procedure that uses a series of x-rays called computed tomography to make a series of pictures of the colon. A computer puts the pictures together to create detailed images that may show polyps and anything else that seems unusual on the inside surface of the colon. This test is also called colonography or CT colonography. Clinical trials are comparing virtual colonoscopy with commonly used colorectal cancer screening tests. Other clinical trials are testing whether drinking a contrast material that coats the stool, instead of using laxatives to clear the colon, shows polyps clearly.

DNA stool test

This test checks DNA in stool cells for genetic changes that may be a sign of colorectal cancer.

Screening clinical trials are taking place in many parts of the country. Information about ongoing clinical trials is available from the NCI Web site 1.



Glossary Terms

abnormal (ab-NOR-mul)
Not normal. An abnormal lesion or growth may be cancer, premalignant (likely to become cancer), or benign (not cancer).
barium enema (BAYR-ee-um EH-neh-muh)
A procedure in which a liquid that contains barium sulfate is put through the anus into the rectum and colon. Barium sulfate is a silver-white metallic compound that helps show pictures of the colon, rectum, and anus on an x-ray.
blood (blud)
A tissue with red blood cells, white blood cells, platelets, and other substances suspended in fluid called plasma. Blood takes oxygen and nutrients to the tissues, and carries away wastes.
cancer (KAN-ser)
A term for diseases in which abnormal cells divide without control and can invade nearby tissues. Cancer cells can also spread to other parts of the body through the blood and lymph systems. There are several main types of cancer. Carcinoma is a cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is a cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is a cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord. Also called malignancy.
cell (sel)
The individual unit that makes up the tissues of the body. All living things are made up of one or more cells.
clinical trial (KLIH-nih-kul TRY-ul)
A type of research study that tests how well new medical approaches work in people. These studies test new methods of screening, prevention, diagnosis, or treatment of a disease. Also called clinical study.
colon (KOH-lun)
The longest part of the large intestine, which is a tube-like organ connected to the small intestine at one end and the anus at the other. The colon removes water and some nutrients and electrolytes from partially digested food. The remaining material, solid waste called stool, moves through the colon to the rectum and leaves the body through the anus.
colonoscope (koh-LAH-noh-SKOPE)
A thin, tube-like instrument used to examine the inside of the colon. A colonoscope has a light and a lens for viewing and may have a tool to remove tissue.
colonoscopy (KOH-luh-NOS-koh-pee)
Examination of the inside of the colon using a colonoscope, inserted into the rectum. A colonoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove tissue to be checked under a microscope for signs of disease.
colorectal cancer (KOH-loh-REK-tul KAN-ser)
Cancer that develops in the colon (the longest part of the large intestine) and/or the rectum (the last several inches of the large intestine before the anus).
computed tomography scan (kum-PYOO-ted toh-MAH-gruh-fee skan)
A series of detailed pictures of areas inside the body taken from different angles. The pictures are created by a computer linked to an x-ray machine. Also called CAT scan, computerized axial tomography scan, computerized tomography, and CT scan.
contrast material (KON-trast muh-TEER-ee-ul)
A dye or other substance that helps show abnormal areas inside the body. It is given by injection into a vein, by enema, or by mouth. Contrast material may be used with x-rays, CT scans, MRI, or other imaging tests.
digital rectal examination (DIH-jih-tul REK-tul eg-ZA-mih-NAY-shun)
An examination in which a doctor inserts a lubricated, gloved finger into the rectum to feel for abnormalities. Also called DRE.
DNA
The molecules inside cells that carry genetic information and pass it from one generation to the next. Also called deoxyribonucleic acid.
fecal occult blood test (FEE-kul uh-KULT...)
A test to check for blood in the stool. Small samples of stool are placed on special cards and sent to a doctor or laboratory for testing. Blood in the stool may be a sign of colorectal cancer. Also called FOBT.
gastrointestinal tract (GAS-troh-in-TES-tih-nul trakt)
The stomach and intestines. The gastrointestinal tract is part of the digestive system, which also includes the salivary glands, mouth, esophagus, liver, pancreas, gallbladder, and rectum.
genetic (jeh-NEH-tik)
Inherited; having to do with information that is passed from parents to offspring through genes in sperm and egg cells.
immunochemical fecal occult blood test (IH-myoo-noh-KEH-mih-kul FEE-kul uh-KULT...)
A test to check for blood in the stool. A brush is used to collect water drops from around the surface of a stool while it is still in the toilet bowl. The samples are then sent to a laboratory, where they are checked for a human blood protein. Blood in the stool may be a sign of colorectal cancer. Also called iFOBT, immunoassay fecal occult blood test, and immunologic fecal occult blood test.
laxative (LAK-suh-tiv)
A substance that promotes bowel movements.
physical examination (FIH-zih-kul eg-ZA-mih-NAY-shun)
An exam of the body to check for general signs of disease.
polyp (PAH-lip)
A growth that protrudes from a mucous membrane.
rectum (REK-tum)
The last several inches of the large intestine closest to the anus.
screening (SKREE-ning)
Checking for disease when there are no symptoms. Since screening may find diseases at an early stage, there may be a better chance of curing the disease. Examples of cancer screening tests are the mammogram (breast), colonoscopy (colon), Pap smear (cervix), and PSA blood level and digital rectal exam (prostate). Screening can also include checking for a person’s risk of developing an inherited disease by doing a genetic test.
sigmoid colon (SIG-moyd KOH-lun)
The S-shaped section of the colon that connects to the rectum.
sigmoidoscope (sig-MOY-doh-skope)
A thin, tube-like instrument used to examine the inside of the colon. A sigmoidoscope has a light and a lens for viewing and may have a tool to remove tissue.
sigmoidoscopy (sig-MOY-DOS-koh-pee)
Examination of the lower colon using a sigmoidoscope, inserted into the rectum. A sigmoidoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove tissue to be checked under a microscope for signs of disease. Also called proctosigmoidoscopy.
stage (stayj)
The extent of a cancer in the body. Staging is usually based on the size of the tumor, whether lymph nodes contain cancer, and whether the cancer has spread from the original site to other parts of the body.
stool (stool)
The material in a bowel movement. Stool is made up of undigested food, bacteria, mucus, and cells from the lining of the intestines. Also called feces.
symptom (SIMP-tum)
An indication that a person has a condition or disease. Some examples of symptoms are headache, fever, fatigue, nausea, vomiting, and pain.
virtual colonoscopy (VER-chuh-wul KOH-luh-NOS-koh-pee)
A method to examine the inside of the colon by taking a series of x-rays. A computer is used to make 2-dimensional (2-D) and 3-D pictures of the colon from these x-rays. The pictures can be saved, changed to give better viewing angles, and reviewed after the procedure, even years later. Also called computed tomographic colonography, computed tomography colonography, CT colonography, and CTC.
x-ray (EX-ray)
A type of radiation used in the diagnosis and treatment of cancer and other diseases. In low doses, x-rays are used to diagnose diseases by making pictures of the inside of the body. In high doses, x-rays are used to treat cancer.

Table of Links

1http://cancer.gov/clinicaltrials